Surface plasmon polariton contributions to strokes emission from molecular monolayers on periodic Ag surfaces

Surface enhanced Raman scattering from molecular monolayers adsorbed on a holographic grating and covered by Ag has been studied. The coupling of surface plasmon polaritons to light through the grating produces emission similar to the continuum observed in other surface Raman experiments. The angular dependence of the surface Raman scattering shows that enhanced Raman cross-sections can arise from scattering of surface plasmon polaritons into light by the localized molecular vibrations.     

近年国内非弹性光散射研究的一些进展

本文介绍了近二年来我国在用喇曼散射和布里渊散射研究半导体、金属及半导体超晶格,高温超导体、磁性物质和介电晶体等方面的进展,以及表面增强喇曼和受激光散射研究的进展情况。     

Surface enhanced Raman scattering of light by ZnO nanostructures

Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E ₂(high) and A ₁(LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 10³) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model.     

Raman effect in the x-ray region

This paper presents a brief review of x-ray Raman scattering and some of our calculations on Raman scattered line shapes from light elements. We summarise the history of the Raman process in the x-ray region and present a detailed theory of the Raman scattering from an atomic many-electron system. Actual calculations of the Raman cross-section using this theory in single-particle approximation are given. The process of internal resonance Raman scattering is also discussed in the same formulation. The Raman cross-section is compared with the cross-sections of other x-ray scattering processes.     

Optimized control of generation of few cycle pulses by molecular modulation

Production of subfemtosecond optical pulses or pulses with predetermined sub-cycle shape of electric field demands a broadband coherent light source of few octaves of bandwidth. Previous work has shown that such a broadband light source can be obtained by the molecular modulation technique. In this article, we review theoretical and experimental improvements in this area: from increasing the efficiency of the generation process by use of hollow waveguides to increasing the number of sidebands generated by the Raman additive technique, or by combined vibrational and rotational Raman generation. We find that stimulated rotational Raman scattering can be either enhanced or suppressed at proper detunings from vibrational Raman resonance in the same molecular ensemble.     

荧光/表面增强拉曼散射双模式纳米光学探针的构建及性能研究

提出一种新型的荧光及表面增强拉曼散射（SERS）双模式光学纳米探针。首先,通过再沉淀-包覆法合成二氧化硅包覆香豆素6的纳米颗粒,再在二氧化硅表面静电吸附多聚赖氨酸分子形成包覆层,随后通过原位还原的方法在多聚赖氨酸壳层复合银纳米颗粒,最后在银纳米颗粒表面吸附拉曼分子即形成双模式纳米探针。该探针通过二氧化硅包覆的荧光分子产生荧光信号,以多聚赖氨酸表面的银纳米颗粒作为SERS增强基底,利用拉曼分子获得SERS信号,实现了荧光及SERS双模式成像。荧光与表面增强拉曼散射相结合的双模式分析技术可同时发挥二者的优点,提高成像的分辨率和灵敏度,在生物医学领域具有重要的应用价值。     

The relationship of angle resolved light scattering from surface optical resonances to the surface enhanced Raman effect

For a given mildly rough Ag surface, the angle resolved pattern bears the same shape for elastic light scattering, for Raman scattering from adsorbed pyridine or cyanide, or for the luminescence background. This result suggests that surface enhanced Raman scattering is closely related to topographically related surface optical resonances.     

Enhancement of Secondary Radiation of Chromophores Adsorbed on the Rough Surface of Thin Silver Films under Conditions of Resonance Excitation

The spectra of giant Raman scattering of light and surfaceenhanced fluorescence of certain chromophores absorbing light in the visible spectrum region are investigated. The factors that have an effect on the enhancement of secondary radiation of chromophores adsorbed on the surface of rough silver films under conditions of resonance excitation are determined. The spectra of mirror reflection of light by the substrates used are considered. The coefficients of diffuse and mirror reflection, absorption, and transmission of light by thin silver films at wavelengths of 488 and 633 nm are determined. The scheme of an experimental system for observation of the spectra of giant Raman scattering and surfaceenhanced fluorescence on the source side of a transparent substrate is proposed. Conclusions on the predominant contribution of the resonance excitation of surface plasmons to the enhancement of the signal of the giant Raman scattering and surfaceenhanced fluorescence of molecules adsorbed on the rough metal surface are drawn.     

基于增强拉曼散射的光子-原子双模压缩态的实现

拉曼散射过程中利用原子系综中初始制备的自旋激发(原子相干性),以及注入与原子系综中初始制备的自旋激发相关联的种子光场都可以极大的提高光场频率转换的效率,实现增强拉曼散射.本文理论上计算了增强拉曼散射过程中原子-光场量子界面的正交分量的量子起伏,得到了相干性导致的增强拉曼散射,只能在一定的范围内稍微提高初始光子-原子的压缩度;而关联增强拉曼散射,能够制备很强的光子-原子间的双模压缩.这样强压缩度的光子-原子量子界面,对于利用光场和原子系统实现量子精密测量研究有着非常重要的应用.     

一种用多色光作为激发源产生拉曼光谱的新算法

探讨用多色光代替激光作为拉曼光源的新型拉曼光谱仪的可能性。根据拉曼光谱原理, 并通过数学分析, 发现当用多色光照射在样品上时, 所得到的散射光经散射频率校正后在不同频率上的强度分布可以写成样品的Raman-Rayleigh联合散射谱和激发光光源的功率谱的卷积。利用傅里叶变换算法,有可能从多色光照射样品所得到的散射光谱中导出样品的拉曼光谱。基于上述原理,可能发展出不用激光的新一代拉曼光谱仪。     

Au nanoplate/polypyrrole nanofiber composite film: preparation,characterization and application as SERS substrate

Without any other additives or additional energy, Au nanoplates have been successfully prepared and integrated simultaneously with the dedoped polypyrrole nanofiber film via the in situ reduction of AuCl₄^– on the film surface. The morphology and structure of the as‐prepared composite film are characterized, and its application for surface‐enhanced Raman scattering is also investigated. It has been found that the morphology of as‐prepared Au nanoplates is dependent on the reaction duration, while the density is dependent on the concentration of AuCl₄^– ions in the reaction process. It is suggested that polypyrrole plays dual reducing and structure‐directing roles during the formation of Au nanoplates. Surface‐enhanced Raman scattering study shows that the Au nanoplates give an intensive and enhanced Raman scattering when 4‐aminothiophenol is used as a probing molecule. The employed approach may shed some light on simultaneously fabricating and immobilizing other noble metal micro/nanostructures with unique morphology. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface plasmon model of surface enhanced Raman scattering

We present a simple model for surface enhanced Raman (SER) scattering, in which enhanced surface charge densities and fields, coupled to light through a metallic grating, are modulated by vibrating molecular potentials. The modulated charge densities produce radiation at the Stokes shifted frequency.     

Enhanced Raman-scattering measurements in low-density supersonic flows

Raman scattering, enhanced by a light trapping cell, has been used to measure temperature and density in the inviscid and viscous regions of the flow from an open-jet supersonic nozzle. Raman temperatures and densities in the inviscid regions are in excellent agreement with static temperatures and densities calculated from measurements of stagnation temperature, stagnation pressure and Pitot pressure.     

镍纳米球腔阵列上吸附分子拉曼散射的表面增强效应

通过聚苯乙烯纳米球为模板制备了规则排列的镍纳米球腔阵列。研究结果表明吸附于镍纳米球腔内的对巯基苯胺的拉曼散射可被极大增强。拉曼散射的表面增强被归因于纳米球腔阵列的协同表面等离子体共振与光的耦合导致的电磁场增强以及纳米球腔结构对电磁场的聚焦效应而使球腔内电磁场能量密度的增大。     

Surface enhanced Raman scattering by CdS quantum dots

Surface enhanced Raman scattering is studied in nanostructures with CdS quantum dots formed using the Langmuir-Blodgett technology. Features due to quantum dot longitudinal optical phonons are observed in the Raman spectra of both free CdS quantum dots and such dots distributed in an organic matrix. The surface enhanced Raman scattering by nanostructures with CdS quantum dots covered by an Ag cluster film is observed experimentally. Applying Ag clusters onto the nanostructure surfaces results in a sharp (40-fold) increase in the intensity of Raman scattering by optical phonons in the quantum dots. It is shown that the dependence of surface enhanced Raman scattering on the excitation energy is resonant with a maximum at the energy corresponding to the maximum absorption coefficient of Ag clusters.     

硅基拉曼放大器增益的理论分析

提出了硅波导中受激拉曼散射信号光获得正增益的理论分析方法,并对关键参量自由载流子寿命和抽运光功率做了分析,得到了可以获得正增益的自由载流子寿命阈值公式,抽运光功率阈值.研究了抽运方式对于硅基拉曼放大器增益的影响,并指出采用双向抽运方式可以使拉曼增益大大提高. 关键词： 硅基放大器 拉曼放大器 抽运方式     

Raman scattering for weakened bonds in the intermediate state: enhancement of low-frequency vibrations

A multimode theory of the Raman scattering in resonance with an electronic transition causing a strong weakening of atomic bonds is proposed. Simple analytical relations between the Fourier transforms of the first- and second-order Raman amplitudes and the absorption are derived. It is predicted that the Raman scattering on low-frequency vibrations will be strongly enhanced. Besides the second-order Raman scattering is also enhanced as compared to the first-order scattering. The Raman excitation profiles show a structure caused by the Airy oscillations. The shapes of the profiles of all vibrations contributing to the weakening bond are the same as a consequence of the strong mode mixing under the virtual vibronic transition.     

Raman scattering using vortex light

We re-examine the theory of Raman scattering in cubic crystals. The unconventional vector potential of vortex light leads to new selection rules. We show that in this novel optical process, (a) silent phonon modes become active and (b) scattering tensors change for ordinary Raman active phonon modes. Calculation based on a simplified model shows that the vortex Raman scattering intensity can be comparable with that of ordinary Raman process.     

Raman scattering enhancement by dielectric spheres

Raman scattering experiments were performed on Si(60 nm)/metal/substrate structures with and without silica microspheres (with a diameter between 0.5 and 5 µm) on top. Raman scattering from the thin Si layer exhibits enhancements (~20) due to the dielectric spheres, where the enhancement factors depend on the diameter of the spheres. The interaction between light and dielectric spheres has been simulated by finite difference time domain calculations (FDTD), wherein particularly the electric energy density (ED) distribution in the thin Si layer was of concern. For microspheres with a diameter less than ~3 µm, the transverse ED distribution (perpendicular to the incident light direction) within the Si layer is characterised by a single peak centered on the optical axis. For larger diameters, a multimodal transverse ED distribution develops where the maximum is not centered on the optical axis. Using an ad‐hoc approach for surface enhanced Raman scattering in combination with the FDTD calculations, the experimental Raman observations are well accounted for. Copyright © 2013 John Wiley & Sons, Ltd.